Modern high performance microelectronic devices (e.g. semiconductor chips) operate at substantially higher temperatures than their predecessors, which can lead to numerous performance and reliability problems. Some devices operate at temperatures high enough to ignite certain materials, presenting a thoroughly unacceptable fire danger. Some materials expand or contract in response to thermal variations at higher rates than other materials. When two or more materials with different coefficients of thermal expansion (CTE) are used in a microelectronic assembly, the extreme variance between operative and inoperative temperatures can cause materials to separate from one another, leading to device failure. High temperatures can also cause some materials to soften, particularly organic sheet materials, leading to structural and/or electrical failures in microelectronic assemblies.
As a result, a microelectronic assembly must be able to efficiently dissipate heat away from a high temperature microelectronic device. When designing and manufacturing electronic assemblies, the materials used to form substrates, packages, and other components closely associated with high temperature microelectronic devices must not only be able to withstand high temperatures without being damaged, but must also be highly thermally conductive.
Some methods used to increase the stiffness and lower the CTE of substrates or substrate core materials, include adding or increasing the amount of ceramic or glass filler (fiber) in the substrate materials. While this provides some benefits, it also reduces the manufacturability of substrates. In particular, it interferes with formation of holes through the substrate, such as plated through holes, by increasing the wear rate of drill bits, increasing the time required to drill holes, and reducing the number of substrates that may be drilled in a single drilling operation. Further, the reliability of the core material can be detrimentally affected by the increased amount of glass or ceramic filler.
Another approach is to use coreless substrates, but these can have problems such as increased warpage, low machinability, and blistering. Current materials and approaches simply do not provide a solution which combines reliability with highly efficient thermal dissipation in high temperature conditions.